1. Field of the Invention
The present invention relates to an electron gun for radio electric wave generators for ultra high frequencies. It relates more particularly to an electron gun delivering an electron beam propagating along cycloidal paths for use in ultra high frequency generators of the cyclotronic resonance maser type.
2. Description of the Prior Art
In generators called cyclotronic resonance masers such as gyrotrons, an electron beam coming from an electron gun is propagated along helical paths which being guided by a uniform magnetic field directed along the axis of the helix. The beam then passes through an electromagnetic cavity resonating at a frequency f.sub.o close to a multiple of the cyclotronic frequency, in which cavity the transverse velocity components of the electrons interact with a transverse electric field component of the wave for giving up their energy thereto. In this case, the beam is essentially propagated parallel to the magnetic field. Now, since the interaction takes place with the transverse velocity component v.perp. of the electrons, the parallel velocity component v.parallel. corresponds then to unused energy. Attempts have therefore been made to eliminate this parallel velocity by proposing a new type of cyclotronic resonance maser using the same interaction between the electrons rotating in a magnetic field and a resonating cavity as the one used in masers of the prior art but characterized by the fact that the velocity of the electrons parallel to the magnetic field is zero or substantially zero throughout the maser whereas a drift velocity exists perpendicular to the magnetic field due to a continuous electric field in the electron gun and the resonating structure.
In this case, however, electron guns of the type comprising a conical cathode and a conical coaxial anode subjected to an axial magnetic field, used in cyclotronic resonance masers such as gyrotrons, are not suitable.